In recent years, due to remarkable technical advancements in solid state image pickup devices for uses in digital still cameras, video cameras and the like, small charge-coupled devices (“CCD”) and similar devices are developed and, with it, a demand of smaller and lighter optical systems are in great demand.
In particular, there is a need for smaller and thinner optical systems to be used on cellular telephones and portable information terminals as they become smaller and thinner. The optical systems used on the cellular telephones and portable information terminals of the prior art have been relatively small and suitable for demands for smaller and thinner units because they were fixed focal point lens systems.
In order to have a zoom lens that provides variable magnifying power on a cellular telephone and a portable information terminal where a smaller and thinner unit is mandatory, it is necessary to have a plurality of lens barrels that are arranged to be able to slide in and out and cause them to collapse into the body when it is not in use in order to make the system thinner. The embodiment of the lens barrels, including the collapsible mount mechanism, becomes more complex as the number of components increases.
In order to improve the above situation, the present invention intends to provide a small, thin, and light zoom lens having a high quality optical capability suitable for being used on cellular telephones and portable information terminals, more specifically, a zoom lens having a zoom ratio of about 2, a depth direction stroke in the incidence direction of the object light between the in-use and the not-in-use (stored) conditions of less than 9 mm, and the longest dimension when it is in-use of less than 30 mm.